Conventional access to the features and services provided by GSM and UMTS networks involves signalling between the mobile terminal and a standard base station (macro base station) that has a dedicated connection to an MSC and provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. GSM or UMTS) transport protocols. There have recently been proposals to allow access to the features and services provided by GSM and UMTS networks by providing additional special base stations (femto base stations), referred to as access points (APs), for example at a subscriber's home or office, in order to increase network capacity and improve coverage. These access points communicate with the core network via IP based communications, such as a broadband IP network, and are typically routed via the Internet.
Many different names have been given to APs, such as home access points (HAPs), micro-base stations, pico-base stations, pico-cells and femto-cells, but all names refer to the same apparatus. APs provide short range, localized coverage, and are typically purchased by a subscriber to be installed in their house or business premises.
It has also been proposed to use APs in the Long Term Evolution (LTE) telecommunications network currently being developed, but not yet implemented. LTE is likely to be the next network implementation after 3G.
An advantage of using an access point connected to the core network via an IP network is that existing broadband Digital Subscriber Line (DSL) connections can be used to link mobile terminals with the network core without using the capacity of the radio access network or transmission network of a mobile telecommunications network. In other words, the AP is integrated into a DSL modem/router and uses DSL to backhaul the traffic to the communication network.
A further advantage is that APs are able to provide mobile network access to areas where there is no radio access network coverage. Thus, they are expected to be particularly beneficial when installed in buildings with poor radio network coverage from the macro network but which have DSL connections. Additionally, an AP could provide UMTS coverage where there is no 3G coverage at all, perhaps only GSM coverage.
Currently, telecommunication network providers sometimes offer subscribers different call tariffs based on their location. For instance, one such service provides subscribers with cheaper tariffs when they use their mobile terminal in their home.
In one known implementation of such a system, upon a subscriber subscribing to a reduced tariff service, the core network identifies which base station(s), and hence which cell(s), provide coverage to the subscriber's home. These base stations are referred to as the subscriber's home base station(s). Each base station has a unique cell ID and the unique cell ID(s) of these home base station(s) are logged against the subscriber's profile. Therefore, when the subscriber is communicating on the mobile network and is located within his home, the subscriber's communication traffic should be routed from the home base station(s), through a Controller (e.g. a Radio Network Controller, RNC in 3G) and onward to the core network.
During the call set up procedure, the core network will receive the MSISDN of the subscriber and the cell ID of the base station with which the subscriber is communicating. In order to confirm at which rate to change the subscriber, the core network checks whether the subscriber is using one of the home base stations which cover his house. This check is made by consulting the Location Based Charging (LBC) Module and by comparing the MSISDN and cell ID identified in the call with those stored in the database. If the cell ID for the MSISDN is the ID of one of the subscriber's logged home base stations, the subscriber is recognised as calling from within his home and is charged at a reduced rate, otherwise he is charged at his standard rate.
With this in mind, APs provide another opportunity for network providers to offer reduced rates to subscribers. For instance, subscribers may benefit from a different call tariff when using their mobile terminal through an AP acting as a base station.
The present inventor has found that when a home base station (either an AP or a macro base station) is provided at a particular location, the subscriber's mobile device may select other base stations when at that location. This may happen, for example, if there is a nearby macro base station that perhaps in some parts of the AP's coverage area, for example the subscriber's, home provides better radio coverage/quality than the home base station.
Mobile networks such as 2G (GSM), 3G (UMTS) and LTE telecommunications networks have an active state of communication with their mobile terminals during which the device and network are exchanging user data, for example during a call or data exchange, and an inactive/idle state of communication with their terminals during which the terminal is not engaged in a call but takes regular network measurements and reports these to the network. When in the active state, as the mobile terminals move between different cells of the network, the communication session is maintained by performing a “handover” operation between the cells. In the inactive/idle state, as a mobile terminal moves between different cells of the network the mobile terminal performs “cell reselection” to select the most appropriate cell on which to “camp” in order that the mobile terminal can be paged by the network when mobile terminating data is destined for that mobile terminal.
Conventionally, the mobile terminal or network determines whether a handover/cell reselection procedure should be triggered in dependence upon measurements of the radio signals of the cells in the region of the mobile terminal. A filter is applied to the signals (either by the network or by the mobile terminal) which calculates an average (mean) value of these signals over a particular time period. This filtered/average values of the cells are then compared with each other or with a threshold value. In dependence upon these comparisons, cell reselection/handover related procedures are triggered. This cell reselection/handover process generally comprises taking radio signal measurements of neighbouring cells and comparing these to each other and to the radio signal of the current cell to determine which cell provides the best signal strength/quality. Handover/reselection to the best cell can then occur.
Handover and cell reselection are performed in the same way for APs as with macro base stations. It is desirable for mobile terminals to provide continuous service when moving within an SAE/LTE coverage area and between an SAE/LTE and a UMTS coverage area/2G coverage area, and to/from APs.
In a mobile network operating in accordance with the 3G (UMTS) Standards, a mobile terminal device (UE) has a so-called “RRC (Radio Resource Control) state” which depends on its state of activity. In the respective RRC states different functions for mobility are executed. These functions are described in technical specification 3GPP TS 25.304/25.331.
For 2G and 3G, a mobile terminal is in active communication when it has a CS (Circuit Switched) connection established.
In 2.5G, GPRS PS (Packet Switched), active communication can be defined as the GPRS Ready state. In 3G UMTS PS, active communication can be defined as the RRC connected mode state that is CELL-DCH.
In 3G UMTS PS, CELL/URA_PCH and CELL_FACH can be defined as inactive states. In GPRS, the Standby state can be regarded as an inactive state.
Either one or both of the CS and PS active communications may occur in the mobile terminal.
For a 3G mobile terminal, in the active mode the terminal is in the RRC connected mode. The RRC connected mode includes the following states:
CELL_DCH state is characterized by:
                A dedicated physical channel is allocated to the UE in uplink and downlink.        The UE is known on cell level according to its current active set        Dedicated transport channels, downlink and uplink (TDD) shared transport channels and a combination of these transport channels can be used by the UE.CELL_FACH state is characterized by:        No dedicated physical channel is allocated to the UE.        The UE continuously monitors a FACH (forward access channel) in the downlink.        The UE is assigned a default common or shared transport channel in the uplink (e.g. RACH) that it can use anytime according to the access procedure for that transport channel.        The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update.        In TDD mode, one or several USCH or DSCH transport channels may have been established.CELL_PCH state is characterized by:        No dedicated physical channel is allocated to the UE. The UE selects a PCH (paging channel) with the algorithm, and uses DRX for monitoring the selected PCH via an associated PCH.        No uplink activity is possible.        The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update in CELL_FACH state.URA_PCH state is characterized by:        No dedicated channel is allocated to the UE. The UE selects a PCH, and uses DRX for monitoring the selected PCH via an associated PCH.        No uplink activity is possible.        The location of the UE is known on UTRAN routing area level according to the URA assigned to the UE during the last URA update in CELL-FACH state.        
In the CELL_DCH state a network-driven handover is performed when necessary, as described in 3GPP TS 25-331. In this state a mobile terminal scans the pilot channels of up to 32 intra-frequency cells neighbouring its current cell. The mobile terminal forms a list of the best cells for possible handover based on the received signal strength and/or quality (i.e. the error rate in the received signal). The information in this list is passed to the UTRAN RNC on an event-driven basis, e.g. when the signal strength or signal-to-noise ratio of one of the cells exceeds a threshold. The information list is used by a handover algorithm implemented in the UTRAN RNC. The algorithm that determines when handover occurs is not specified in the GSM or UMTS Standards. The algorithms essentially trigger a handover when the mobile terminal provides a measurement of a neighbour cell received signal at the mobile terminal below a predetermined quality received threshold, which typically has a relation to the quality of the received signal from the serving cell (e.g. better quality by some margin).
In the “CELL_FACH”, “CELL_PCH”, “URA_PCH” or “idle mode” the mobile terminal controls its own mobility independently and starts a cell switch (reselection) when a neighbouring cell has a better quality than the current cell, as described in 3GPP TS 25.304. A similar procedure is also used in GSM/GPRS mobile networks, as described in technical specification 3GPP TS 05.08 (UE-based cell reselection).
In general, a mobile terminal in “idle mode” states and in RRC connected mode (inactive) states “CELL_FACH”, “CELL_PCH” and “URA_PCH” performs periodic measurements of its own as well as of a series of neighbouring cells. Information from the neighbouring cells is broadcast in the system information block 11 (SIB11) or system information block 12 (SIB12) of the broadcast channel (BCH) as described in 3GPP TS 25.304 and 3GPP TS 25.331.
In order to avoid a cell reselection/switch based on short-term changes in the radio field conditions, so-called “fading”, and the subsequent return to the original cell, a UMTS system mainly uses two parameters that are emitted in the Broadcast Channel (BCH) in the system information block 3 (SIB3) or system information block 4 (SIB4). Notably, these are the time interval “Treselection” and the hysteresis value “Qhyst”. In order to avoid too fast a switch between cells based on quickly changing network conditions, a switch from the original cell to the neighbouring cell only takes place if the neighbouring cell was better than the original cell by the factor “Qhyst” for the time “Treselection”. This behaviour of a mobile end device is described in detail on the technical specification 3GPP TS 25.304. Multiple frequency layers and mobility state determination are provided in a similar manner for LTE/SAE networks.
When a subscriber is at their home location, the reselection measurements continue to be made in the normal way and cell reselection may occur. When a base station other than the home base station is selected, this is unsatisfactory for several reasons. Firstly, if the home base station is an AP, the capacity of the macro network will be used unnecessarily. Secondly, the subscriber will not receive the discounted “home” rate when using a base station other than the macro network. This is a particular problem as the subscriber is unlikely to be aware of which base station is selected. Therefore, it is preferable to keep the subscriber on their AP rather than for their terminal to reselect to a macro cell.
One solution would be to increase the power of the home base station but this has the disadvantages of increasing interference to neighbouring base stations and reducing bandwidth.
Accordingly, it would be desirable to provide an alternative solution, without these disadvantages.